Potential induced degradation (PID) a photovoltaic cell panel means that when the photovoltaic cell panel is used, if there is a bias voltage between the cell panel and earth PE, output power degradation occurs in the cell panel after a period of time.
Various mechanisms result in such degradation. For example, under an effect of the foregoing voltage, ion migration occurs in a packaging material of a cell of a component and a material of an upper surface layer and a lower surface layer of the component, hot carrier occurs in the cell, an active layer of the cell is reduced due to redistribution of charges, and a related circuit is corroded. These mechanisms resulting in degradation are referred to as potential induced degradation, polarization, electrolytic corrosion, and electrochemical corrosion. In recent years, PID has become one of important factors contributing to complaints of foreign buyers against quality of components from China. When PID is serious, power of a component may be degraded by at least 50%. Consequently, power output of an entire power station is affected.
To resolve PID degradation, in other approaches, a virtual neutral (N) point is constructed using an inverter circuit, a positive electrode or a negative electrode of a bus of the inverter circuit is grounded, and a bus voltage is adjusted, to implement a bias voltage to earth of a positive electrode or a negative electrode of the cell panel string, thereby resolving PID degradation. In the method, because a minimum of a half-bus voltage is a half of an uncontrolled rectified voltage of a power grid voltage, a compensation range is narrow. In addition, at a moment when the bus is grounded, the cell panel string has parasitic capacitance to earth, generating a surge current. Consequently, an inverter is shut down due to an excessively large leaked current, affecting a power generation capacity of the entire power station.